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Old January 15, 2009, 05:05 PM   #1
Join Date: January 15, 2009
Location: Murray, KY
Posts: 16
Revolver tolerances?

Hey guys,

I'm new to the forum and I was reading a thread in another section where a guy had bought a new-in-box revolver that was out of spec. I only own one wheelgun at this point, but I plan on adding others. I do own a set of feeler gauges so I thought I might as well check mine.

I have a Smith and Wesson PC 327 TRR8 (yeah I know - expensive and ugly to some, but I like it). Can one of you tell me what the barrel to cylinder gap, headspace, and any other critical measures you can think of should be? I am interested in learning more about gunsmithing so feel free to treat me like a student and elaborate on these measures as much as you like.

Thanks guys!
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Old January 15, 2009, 05:37 PM   #2
James K
Join Date: March 17, 1999
Posts: 24,189
The b/c gap should be .006-.008" with .007 as close to ideal IMHO). S&W specs allow up to .010", and I wouldn't worry if it went that high, but it would not be my preference. (Most folks concentrate on the b/c gap not being too great, but they forget that if it is too little, the cylinder can bind up from both crud and from expansion when firing if it gets very hot.)

As to headspace, I used to know what it was for .38 Special/357 but I can't find the papers now. In a revolver it can be checked with feeler gauges.

Jim K
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Old January 15, 2009, 09:09 PM   #3
Harry Bonar
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I agree with Jim but personally I like mine a little tighter.
The main thing you must have to get your "tolerances" tight is a correct adjustment of crane play - there should be NONE - ZERO! When you close your cylinder look to the front line where it meets the rest of the frame and by GENTLY pushing out there should be NO gap seen. (I know this is rare Jim) then there should be no end shake (none that he can feel Jim) - there will normally be .001 to .002 there but you cannot feel it when lubricated properly.
Then, you can MAINTAIN the measurements for headspace and cylinder gap..
Now, most of the noise in shooting a revolver comes from the barrel/cylinder gap! To me I like a maximum (with the former specs met) of no more than .004 with an absolute maximum of .006 and as far as headspace there shouldn't be more than that with different brands of ammo (head thickness might vary).
The next check would be with a "range rod" to see how the bore/cylinder line-up is. And, if you have the tools to do it make sure the bbl is aligned with the frame.
Now, with deference to Jims excellent post I will tell you that it will be rare to find any D/A revolver that meet these specs.
Harry B.
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Old January 15, 2009, 11:11 PM   #4
James K
Join Date: March 17, 1999
Posts: 24,189
Hi, Harry,

It is like a lot of other things. No mass produced item can possibly be as tightly fitted as one that is virtually made by hand by a master craftsman. The problem for most of us is that we can't afford what the craftsman charges.

I think .004" is a bit tight if you shoot the gun a lot in a short time. Even 50 rounds of rapid fire can expand the cylinder enough to bind at .002", so maybe .004" would be OK but I like to allow a bit for dirt and crud.

And BTW, MOST of the noise from a revolver comes from the end of the barrel, not the b/c gap; FWIW, a suppressor will work on a revolver, just not as well as on a pistol without the gap.

Jim K
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Old January 15, 2009, 11:34 PM   #5
Join Date: March 4, 2005
Location: Ohio
Posts: 13,814
Agree with both the gentlemen, above. I always set my Dan Wesson (that gun's gap is adjustable) up for 0.003"-0.004" B/C gap for target shooting, even though the gauge that came with it was 0.006". I used 0.006" for .357 loads or for double-action practice where the pace and heat picked up over bullseye match pace. In other words, the bigger number was for reliability in combat type shooting, the smaller one was to help low pressure target loads maintain pressure uniformity fired at a modest pace. I never had a malfunction from the narrower gap, but it never went very long without cleaning in its target capacity.

When I bought my Ruger Redhawk years ago, the shop had three of them they had just received sitting in the display case. I had not gone in expecting to buy anything, but at the sight of them, temptation took hold. I had no tools with me, but I checked cylinder play as Harry describes, by feel. I checked all three with the thumb drag test*. I held them all up to a light and made sure the barrel cylinder gaps were parallel-sided and even. I hope it goes without saying that I checked to be sure there was no ammunition in the guns when I first picked them up, but a double check before the next step was in order: I put a strip of white paper between the cylinder and recoil plate and held it so some light fell on the paper. I looked down the bore while cocking the hammer. I checked to see which gun's chambers were best centered in the barrel when in battery. One was perfect, and that's the one I bought.

Below is an early 50 yard group from that Redhawk fired off bags using a low power Burris scope. I don't know why I didn't date it? It is circa 1986. The American Eagle ammunition would have been the first box I bought for it. One chamber in the gun is a little too tight and always throws the one flier you see in the group below. I've considered reaming the cylinder, but I don't want to mess with the success of the first five chambers, and buying a specially ground reamer to match the sixth to the other five is a bit spendthrift for my taste. I just don't use the sixth chamber.


*Drag thumb lightly on cylinder while cocking the hammer to be sure the hand rotates the chambers enough for the bolt to snap in and lock up every chamber. One of the three failed this last test on two chambers, so it was weeded out.
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